In a hierarchical model of a database, items of information or data are represented by a tree-and-branch structure. This model of a database emphasizes the superior-inferior relationships between information items and is very suitable for data wherein such relationships are inherent, e.g., organization charts.
More specifically, a hierarchical database is defined as an ordered set of data wherein elements of data in the set are composed of different occurrences of a single type of database format. An occurrence in turn comprises an ordered arrangement of segments of data and, finally, a segment is defined in terms of a set of associated fields.
Oftentimes to satisfy updated design specifications, particularly in the development of large software systems, it is necessary to transition an existing database to a new database, usually by rearranging, modifying such as by additions and deletions or restructuring the existing database. Broadly speaking, the transitioning process converts field occurrences in the existing or input database to different field or segment occurrences in the new or output database.
With conventional conversion approaches, whenever database transitions are required, new database-specific transition software has been developed and tested each time the existing database is converted. For large system developments, this is inefficient since a significant portion of the programming effort and budgetary expenditure is devoted to the development of each database-specific transition.